In the field of endoscopy, for example, the functional limit of endoscopes used as present are defined by their rigidity or flexibility. The rigid instruments examine only a relatively short distance; the flexible sondes probe much farther but have to use the lumen of the tract into which they are inserted as a guide. Stiffening wires and tubes have been employed to facilitate passage of the colonoscope, and the success of these devices in clinical trials demonstrates that a sonde of controlled compliance is desired. Examples of flexible endoscopes are illustrated and described in U.S. Pat. No. 3,572,325 issued Mar. 23, 1971, U.S. Pat. No. 3,190,286 issued June 22, 1965, U.S. Pat. No. 3,799,151 issued Mar. 26, 1974, and U.S. Pat. No. 3,583,393 issued June 8, 1971.
The angular control of the distal tip of presently known endoscopes does little to help transmit the operator's push at the proximal end in the general direction of the tract to be followed. The flexible finger at the tip provides only an increase in the field of view and is of limited use of directional control. The advance of the endoscope through loops in the lower large bowel can, at times, be assured only by "hooking" the tip over a flexure. It is, of course, very difficult to estimate the pull on the mesenterium during these maneuvers but it stands to reason that the shearing force acting on the mucosa directly underneath the hook is greater and more serious in its consequences than the slight pressure necessary to deflect the sonde's head from the intestinal wall in order to direct it down the lumen.
In fields other than endoscopy, or even than the field of body examination and treatment, there is a need for a device which is capable of being inserted in a passageway having many flexures and which may be driven in a snake-like manner in this passageway by simply controlling it by its proximal end.